High frequency heating generator for microwave ovens



Aug. 9, 1966 P. w. CRAPUCHETTES 3,

HIGH FREQUENCY HEATING GENERATOR FOR MICROWAVE OVENS F'iled Aug. 14, 1961 2 Sheets-Sheet 1 flawa/ se 9, 1966 P. w. CRAPUCHETTES 3,265,850

HIGH FREQUENCY HEATING GENERATOR FOR MICROWAVE OVENS Filed Aug- 14, 1961 2 Sheets-Sheet 2 The present invention relates to power units for micro wave heating purposes and more particularly to a selfcontained microwave power unit.

In the cooking of food or the heating of other lossy' dielectric material, microwave heating units are becoming increasingly important. To indicate the convenience of microwave ovens, a roast, for example, may be taken from the freezer and completely thawed and cooked in 15 or 25 minutes.

In the microwave cooking field magnetrons are generally employed as the source of high frequency energy. A magnetron characteristically includes a central axially disposed cathode, and a conductive anode surrounding the cathode which includes a series of cavities which open toward the cathode. For proper operation from commercially available alternating current, magnetrons require a step-up transformer and a rectifier including filter circuits. Magnetic coils are also usually included to supply the :axial magnetic field betweenthe cathode and anode which is necessary for oscillation.

Many arrangements, including magnetron oscillators, have been proposed up to the present time for supplying microwave energy for heating purposes; however, the prior designs have frequently been wasteful of energy, in that prolonged transmission paths are required. In addition, the long waveguide transmission paths and the air-cooled designs which have been employed, take up unnecessary space.

Accordingly, principal objects of the present invention include reducing the required space and cost, and increasing the efficiency of microwave heating units.

These objects are achieved in accordance with the present invention by combining the microwave tube struc ture and the power supply into a single unitary device which is preferably liquid-cooled.

In accordance with one important aspect of the invention, the microwave power unit is provided with a magnetic outer casing, and this casing forms the return path for the biasing magnetic field of the magnetron tube which generates the microwave energy. In accordance with a collateral aspect of the invention, both the magnetron and the components of its associated power supply unit, may be immersed in cooling fluid such as oil which fills most of the magnetic casing. Suitable expansion arrangements such as bellows or the like may be provided to accommodate changes in the volume of the oil which is employed.

In accordance with still another feature of the invention, the biasing magnetic field for the magnetron tube may be supplied by two symmetrically arranged coils which are also included in filtering circuits which supply the direct current to the magnetron.

In accordance with another aspect of the invention, mode stirring or mixing within the microwave oven may be achieved by a movable radiating element which is actuated by at least one of the magnetic coils associated with the magnetron tube structure.

Advantages of the device as described above include reduction in the size of the power supply and the magnetron equipment and great reduction in the cost. These economies are produced first by the use of a single liquid cooled assembly and second, by the compact arrangement which may be achieved when all of the components are I United States Patent combined in a single sealed housing. It is contemplated that the resultant unit may be widely used for microwave heating purposes, as the only special installation requirement is a circular opening in one wall of the oven.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of construction and operation, together with further objects and advantages thereof. will be better understood from the following description taken in connection with the accompanying drawing in which illustrative embodiments of the invention are disclosed, by way of example. It is to be expressly understood, however, that the drawing is for the purposes of illustration and description only and does not constitute a limitation of the invention.

In the drawing:

FIG. 1 shows a microwave heating power unit in accordance with the invention;

FIG. 2 shows the circuit diagram of the power pack unit of FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is a view of a movable radiating element taken along line 4-4 of FIG. 1;

FIG. 5 represents an alternative transformer arrangement, in accordance with the present invention; and

FIG. 6 illustrates the use of the power pack shown in FIGS. 1 through 5 of the drawing in combination with a microwave oven structure, in accordance with the invention.

With reference to the drawings, FIG. 1 shows a microwave power pack 12 having an outer casing 14. It is secured in position by the bolts 16 and 18 which extend through the flange 20 into the wall 24 of an oven. The microwave unit 12 includes the protruding portion 26 which extends into the opening 22 to a position approximately flush with the inner surface of the oven. In operation, microwave energy from the magnetron tube structure 28 is coupled to the radiating element 30 forming part of the protruding structure 26, and high intensity microwave energy is introduced into the oven.

The power pack 12 includes, within the outer casing 14, the magnetron tube 28, several capacitors including a large capacitor 32, two power rectifiers 34 and 36, and a transformer structure 38. To facilitate cooling of the electrical apparatus within casing 14, it is filled with oil. The transformer 38 may be supported by spaced brackets 38 to permit free flow of the cooling oil between the transformer and the wall of the casing. As the oil is heated during operation, it expands. In order to accommodate this change in volume of the oil, the bellows 40 is provided with flexible outer walls 42 so that the lower surface 44 of the bellows approaches the upper wall 46 of the unit 12 when the oil expands upon heating. The opening 48 permits the passage of atmospheric pressure into the bellow structure 40; accordingly,

ture 38, provides filament power to the magnetron 28.

The voltage doubling rectifier circuit shown in FIG. 2 includes the two diodes 34 and 36 in addition to the filter circuits 58 and 60 and the high voltage storage capacitor 32. The filter circuit 58 includes the coil and a capacitor 61, and the filter circuit 60 includes the coil 52 and a capacitor 62. The arrows 64 and 66 are shown associated with the coils 50 and 52 as well as the magnetron 28, to indicate the physical association of these three components as discussed above in connection with FIG. 1.

The capacitors 61 and 62 tune the resonant circuits 58 and 60 to a frequency such as 20 or 30 cycles, well below the 60-cycle frequency of the applied power. The input capacitor 68 is employed to couple alternating current to the voltage doubling stage, in accordance with conventional usage in cascade voltage doublers as disclosed,

for example, at pages 592 and 593 of F. E. Termans Radio Engineers Handbook, McGraw-Hill, 1943.

The cross-sectional view of FIG. 3 is taken along line 33 of FIG. 1. FIGS. 1 and 3, taken together, serve to indicate the physical relationship of the circuit components of FIG. 2. Thus, the large storage capacitor 32 which supplies plate voltage to the magnetron 28 is oated on one side of the magnetron structure. The three smaller. capacitors 61, 62 and 68 may be located on the other side of the magnetron structure, with the capacitor 61 located close to coil 50 with which it is associated and the capacitor62 being located close to coil 52.

The structure of the magnetron 28 will now be considered. Initially, it is noted that the structure is patterned after the arrangement disclosed in B. Kumpfer US. patent application Serial No. 21,302, filed April 11, 1960, and entitled Magnetron Device. Specifically, the tube 28 includes a vacuum tube envelope having two conductive end members 72 and 74 and an insulating member 76 of refractory material. The cylindrical member 76 is preferably made of a material which is of high heat conductivity and which is transparent to microwaves. One suitable material which has been employed for this purpose is beryllium oxide. The anode structure includes an electrically conductive cylinder 78 in engagement with the cylinder 76, and a plurality of radially extending vanes indicated at 80 and 82. The vanes 80 and 82 may include small protruding elements or tabs 84 and 86, respectively, for engagement with conventional strapping rings 88 and 90. As is customary, the strapping rings 88 and 90 engage alternate sets of vanes, respectively. The cathode 92 may be in the form of a helical wire which is mounted in place between the heads of the screws 94 and 96 which extend through and are sealed to the conductive end plates 72 and 74 of the magnetron 28.

The magnetic circuit of the magnetron 28 will now be considered. In this connection, it is desirable that a steady axial magnetic field be applied to the magnetron 28, particularly in the space between the cathode 92 and the ends of the vanes 80 and 82 which extend radially from the cathode to the anode cylinder 78. The desired magnetic field is provided by the coils 50 and 52 which are mounted on the magnetic pole pieces 102 and 104, respectively. The return magnetic circuit is provided through the curved magnetic members 106 and 108 which are secured to the pole piece structures 102, 104, respectively, and by the casing 14 of the power pack, which is also made of magnetic material.

The magnetic members 106 and 108 are separated from the housing-14 by insulating spacers 110 and 112, respectively. Power for energizing the cathode 92 may therefore be connected to the metal end plates 72 and 74 without short-circuiting through the metal housing 14.

The mode of coupling high frequency energy from the magnetron 28 to the oven will now be considered in some detail. The coupling structure is shown in detail in FIG. 1. The coupling structure includes a radiating element 30 and a generally conical conductive horn structure 114. The radiating element 30 is coupled to the anode structure by a loop 116 and a conductor 128 which is sealed through openings in the refractive cylinder 76 and the cylindrical anode member 78. In FIG. 1, the coupling loop 116 appears in front of one of the radially extending vanes 80'. The radiating element 30 is held rigidly in place and is bonded to the insulating window 118 through which the microwave energy is transmitted into the stove.

A fixed pattern of standing waves produces an uneven cooking pattern within an oven. To avoid this adverse effect, a mode mixing apparatus is provided as an integral part of the power pack 12. The mode mixing structure includes a conductive element 120 secured to an insulating member 122, which is in turn mounted on a magnetic spring 124. The spring 124 forms the armature of a vibrating electromagnetic structure which is tuned to the 60-cycle frequency at which current pulses are supplied to the electromagnet 50. A magnetic pole piece extension member 126 extends from a point close to the magnetic member 106 and the housing 14 of the power unit to a point in proximity to the free end of the magnetic reed 124. As 60-cycle pulses pass through the electromagnet 50, magnetic pulses are supplied through member 126 to set the reed 124 into vibration. As reed 124 vibrates, the conductive element moves to and fro and significantly changes the radiation pattern from the element 30. This action produces changes in the standing wave pattern within the oven and provides the mode mixing which is desirable for uniform cooking.

The detail drawing of FIG. 4 shows elements 120, 122 and 128 as viewed along line 4-4 of FIG. 1. The conductor 128 which interconnects loop 116 and the radiating element 30 is enclosed by the two legs of the supplemental radiating element 120. As the element 120 vibrates under control of the magnetic reed 124, the radiating pattern will clearly be changed.

As mentioned above, the main part of the power unit 12 is filled with a cooling fluid such as oil. The bellows unit 40 and the radiating horn 114 are free of oil, however. Thus, the oil is sealed above the magnetic plate 126 and the insulating material 129 at the bottom of the main portion.

FIG. 5 shows an alternative arrangement for the autotransformer 38 and the bellows unit 40. These components in the cross-sectional View of FIG. 5 are therefore designated by the reference numerals 38 and 40. The

autotransformer structure of FIG. 5 has a magnetic core i of D form. It includes a central leg 132 and a semicircular portion 134. In addition, of course, the casing 14 of the structure forms part of the return circuit for the unit. The bellows 40 is of the same form shown in FIG. 1 but is located conveniently to one side of the transformer 38. To avoid unnecessary modulation of the magnetron, the magnetic core member 132 may be mounted perpendicular to the axis of the magnetic members 102 and 104 of the magnetron.

FIG. 6 shows an assembly in which the power pack 12 is mounted on the upper surface of an oven 136. The entire inner surface of the oven 136 is of conductive material. The radiating horn of the power pack 12 extends to a position flush with the inner surface of the upper wall 24 of the oven 136. A conventional oven 'door 138 provides access to the oven, and suitable insulating racks such as the rack 140 are provided for supporting food to be cooked at suitable distance from the walls of the microwave oven.

In accordance with one particularly interesting feature of the invention, the magnetic coil structure of the power unit performs several functions and is uniquely incorporated into the electrical and magnetic circuits of the unit. Thus, for example, the coil 50 performs both a filtering function for the magnetron plate circuit and also actuates the movable mode mixing structure. The structural location of the coils 50 and 52 is also unique in that the magnetic casing of the unit forms the return path for the unidirectional biasing magnetic field for the magnetron.

It is to be understood that the above-described arrangements are illustrative of the application of the principles devised by those skilled in the art without departing from the spirit and scope of the invention. Thus, by way of example, and not of limitation, other known forms of magnetron structures may be employed in place of that shown in the present drawings; other rectifier circuits such as bridge type or voltage multiplication rectifiers may be used; in addition, minor changes in the arrange ment of the components may be effected; and furthermore, two or more of the power pack units 12 may be mounted on the sidewalls or the top of an oven structure in place of the single top-mounted uni-t shown in FIG. 6. Accordingly, it is to be understood that the present invention is to be limited only by the spirit and scope of the appended claims.

What is claimed is:

1. A microwave power unit comprising a magnetron, two magnetic coils mounted to provide a biasing magnetic field rfor said magnetron and a casing of magnetic material for said power unit located in theret'urn magnetic path of said magnetic coils, a radiating element coupled to said magnetron, a movable conducting mode mixing element located in proximity with respect to said radiating element, and means for coupling pulses of energy from one of said magnetic coils to move said mode mixing element.

2. In combination, a magnetron, means including at least one magnetic coil for providing a biasing magnetic field for said magnetron, a rectifier, means for supplying alternating current to said rectifier, a filter circuit including said magnet coil coupled to supply plate current to said magnetron, means for coupling rectified current from said rectifier to .said filter circuit, a mode mixer, and means for actuating said mode mixer in accordance with pulses passing through said magnetic coil.

3. In combination, a magnetron, at least one magnetic coil for providing a biasing magnetic field for said magnetron, a rectifier, means for supplying alternating current to said rectifier, a filter circuit including said coil coupled to supply plate current to said magnetron, mean-s for coupling rectified current from said rectifier to said filter circuit, a mode mixer, and means including an armature coupled to said magnetic coil for actuating said mode mixer in accordance with pulses passing through said magnetic .coil.

4. A microwave power unit comprising: an outer magnetic casing; a microwave energy utilization device; means for securing said magnetic casing to said device; a stepup transformer, a rectifier circuit, a filter circuit including at least one coil, and a magnetron, all mounted within said casing; means for connecting alternating current from said transformer to said rectifier circuit; means for applying direct current from said rectifier and filter circuit to said magnetron; means for mounting said filter circuit coil in proximity to said magnetron to apply a biasing magnetic field to the magnetron; and means including magnetic material for closing the magnetic circuit for said coil through said magnetic casing.

5. A'microwave power unit comprising: an outer magnetic casing; a microwave energy utilization device; means for securing said magnetic casing to said device; a stepup transformer, a rectifier circuit, a filter circuit including at least one coil, and a magnetron, all mounted within said casing; means for connecting alternating current from said transformer to said rectifier circuit; means for applying direct current from said rectifier and filter circuits to said magnetron; means for mounting said filter circuit coil in proximity to said magnetron to apply a biasing magnetic field to the magnetron; means for closing the magnetic circuit for saidcoil through said magnetic casing; a radiating structure extending from the side of said unit which is to be connected to said utilization device; movable means for changing the radiation pattern from said structure; and means for actuating said movable means in accordance with pulses through said coil.

6. A microwave power unit comprising: an outer magnetic casing; an oven; means for securing said magnetic casing to said oven; a step-up transformer, a rectifier circuit, a filter circuit including at least one coil, and a magnetron, all mounted within said casing; means for connecting alternating current from said transformer to said rectifier circuit; means for applying direct current from said rectifier and filter circuits to said magnetron; means for mounting said filter circuit coil in proximity to said magnetron to apply a biasing magnetic field to the magnetron; means for including magnetic material for closing the magnetic circuit for said coil through said magnetic casing; cooling fluid filling said casing; a bellows mounted in one wall of said casing for accommodating changes in the volume of said fiuid; a radiating structure extending from one side of said unit; movable means for changing the radiation pattern from said structure; and means for actuating said movable means in accordance with pulses through said coil.

7. A microwave power unit comprising: an outer magnetic casing; an oven; means for securing said magnetic casing to said oven; a step-up transformer, a rectifier circuit, a filter circuit including at least one coil, and a magnetron, all mounted within said casing; means for connecting alternating current from said transformer to said rectifier circuit; means for applying direct current from said rectifier and filter circuits to said magnetron; means for mounting said filter circuit coil in proximity to said magnetron to apply a biasing magnetic field to the magnetron; means for including magnetic material for closing the magnetic circuit for said coil through said magnetic casing; cooling fluid filling said casing; a bellows mounted in one Wall of said casing for accommodating changes in the volume of said fluid; a radiating structure extending from the side of said unit adjacent said oven; movable means for changing the radiation pattern from said structure; and means for actuating said movable means in accordance with pulses through said coil to change the standing wave pattern within said oven.

References Cited by the Examiner UNITED STATES PATENTS 2,232,559 2/1941 Rice 325-121 2,450,629 10/ 1948 Bondley 313 X 2,648,772 8/1953 Dawson et a1 331-86 2,750,565 6/ 1956 Mercer et a1. 31339 X 2,909,635 10/1959 Haagensen 219-1055 2,979,671 4/1961 Schall 32'8262 X JOHN W. I-I-UCKERT, Primary Examiner.

DAVID J. GALVIN, Examiner.

R. F. POLIS'SACK, Assistant Examiner. 

1. A MICROWAVE POWER UNIT COMPRISING A MAGNETRON, TWO MAGNETIC COILS MOUNTED TO PROVIDE A BIASING MAGNETIC FIELD FOR SAID MAGNETRON AND A CASING OF MAGNETIC MATERIAL FOR SAID POWER UNIT LOCATED IN THE RETURN MAGNETIC PATH OF SAID MAGNETIC COILS, A RADIATING ELEMENT COUPLED TO SAID MAGNETRON, A MOVABLE CONDUCTING MODE MIXING ELEMENT LOCATED IN PROXIMITY WITH RESPECT TO SAID RADIATING ELEMENT, AND MEANS FOR COUPLING PULSES OF ENERGY FROM ONE OF SAID MAGNETIC COILS TO MOVE SAID MODE MIXING ELEMENT. 